Post write erase conditioning
View Patent ↗A storage device with a charge trapping (CT) based memory may include improved data retention performance. Data retention problems, such as charge loss in CT memory may increase for a particular programmed state when a neighboring state is at erased state. Modifying the erase state with post write erase conditioning (PWEC) by pushing up deeply erased states can reduce the lateral charge movement and improve high temperature data retention. In particular, the erase state may be reprogrammed such that the erase distribution is tighter with a higher voltage.
1. A method of conditioning charge trap memory, the method comprising:
programming at least a portion of a block in a charge trap memory;
identifying deeply erased cells from the at least the programmed portion of the block of the charge trap memory; and
reprogramming the deeply erased cells,
wherein the reprogramming comprises reprogramming the deeply erased cells
within a closed block that has its wordlines fully programmed.
2. The method of claim 1 , wherein the identifying deeply erased cells comprises:
performing a read operation on a wordline;
comparing, based on the read operation, a voltage of each erase state for a cell with a threshold value;
identifying a cell as deeply erased when the voltage of that cell is below the threshold value; and
iteratively cycling through each wordline of the block for identifying each of the deeply erased cells in the block.
3. The method of claim 2 , wherein the threshold value comprises 0 Volts, such that each deeply erased cell has an erase state below 0 Volts.
4. The method of claim 1 , wherein the reprogramming narrows a distribution of an erase state for each of the deeply erased cells.
5. The method of claim 4 , wherein the reprogramming comprises applying a voltage to the deeply erased cells that narrows and shifts the distribution of the erase state for each of the deeply erased cells.
6. The method of claim 5 , wherein the voltage is applied through a dumb pulse.
7. The method of claim 5 , wherein the voltage is applied through a verify pulse that comprises a program voltage and a verify operation to verify a voltage after the program voltage.
8. The method of claim 1 , wherein the charge trap memory comprises a dielectric layer for trapping electrons, wherein the dielectric layer is a silicon nitride film.
9. The method of claim 8 , wherein the charge trap memory comprises a metal oxide nitride oxide semiconductor (MONOS) capacitor structure.
10. The method of claim 1 , wherein the charge trap memory comprises a three-dimensional (3D) NAND memory configuration, and wherein a controller is associated with operation of and storing to the charge trap memory.
11. The method of claim 1 , wherein the reprogramming improves data retention by increasing a voltage level and narrowing a distribution of an erase state for the deeply erased cells.
12. The method of claim 1 , wherein the identifying is performed wordline by wordline through the block after the block has been closed.
13. A storage device comprising:
a memory comprising one or more programmed blocks for data storage, wherein the memory comprises a dielectric layer for charge trapping;
a controller coupled with the memory and configured to identify deeply erased cells from the one or more programmed blocks of the memory; and
a recondition circuitry configured to reprogram the deeply erased cells within a closed block that has its wordlines fully programmed.
14. The storage device of claim 13 , wherein the recondition circuitry is part of the controller, and wherein the controller is configured to perform reprogramming the deeply erased cells.
15. The storage device of claim 13 , wherein the recondition circuitry is configured to reprogram the deeply erased cells within an open block that not all of its wordlines are fully programmed, and wherein the reprogram is performed on wordlines of the open block that have programmed data.
16. The storage device of claim 13 , wherein the memory comprises a charge trap flash memory with the charge trapped in the dielectric layer.
17. A memory system comprising:
means for identifying deeply erased cells from at least a programmed portion of a block in a charge trap memory; and
means for reprogramming the deeply erased cells within a closed block that has its wordlines fully programmed.
18. The memory system of claim 17 , further comprising means for identifying a block that is fully programmed and closed.
19. The memory system of claim 17 , further comprising means for identifying a block that is not fully programmed and open.